The Influence of Fire on Saltatoria Diversity in Coastal Habitats Near Pangani,Tanzania (East Africa)

ECOTROPICA 11: 53–61, 2005 © Society for Tropical Ecology THE INFLUENCE OF FIRE ON SALTATORIA DIVERSITY IN COASTAL HABITATS NEAR PANGANI,TANZANIA (EAST AFRICA) Claudia Hemp Dept. Animal Ecology II, University of Bayreuth, 95440 Bayreuth Abstract. In burnt coastal grasslands, fire-disturbed forest remnants, and undisturbed coastal forests of the Pangani area (Tanzania) 61 Saltatoria species were recorded. Comparing open-land habitats with forest and forest edge habitats, diversity rises in open-land habitats, as nearly 60% of the recorded species were found within grasslands. However, the share of endemic and near-endemic species decreases, as only 5% of the species occurring in open-land habitats were endemics, 14% are distributed throughout East Africa, and the majority (81%) are widespread forms. Forest and forest edge habitats, on the other hand, had 60% endemic species, 32% species restricted to East Africa, and only 8% widespread Saltatoria. The majority of the coastal endemics are highly endangered by the ongoing destruction of indigenous forest. Tangana asymmetrica was one of the few coastal endemics that also occurred in fire-influenced forest remnants, while most other forest species were exclusively found in closed undisturbed forest communities of the Gendagenda forest reserve. The new record of Parepistaurus pygmaeus in the Gendagenda reserve offers an explanation of the hitherto disjunct distribution of this flightless species. Accepted 15 June 2005. Key words: Biodiversity, conservation, endemism, fire influence, indigenous tropical lowland forest, Orthoptera, Saltatoria, Tanzania, tropical coastal grasslands. INTRODUCTION lived in the area, mostly farmers, cultivating the fields intensively with bananas, maize, sweet potatoes, ma- The forests along the Kenyan and Tanzanian coast are nihot etc. (Koponen 1994). the remains of a once widespread forest cover. Today Away from the main centers of cultivation around this forest has largely gone, leaving around 250 patches of forest, most of which are less than 500 ha in size Pangani the coastal area was probably little populated. (Burgess & Clarke 2000). The coastal forests, together Most of the coast and hinterland was densely forested. with the adjacent forests of the Eastern Arc Mountains, Clearing by fires was practised from the 19th century are hotspots of endemism due to a constant climate onwards, reducing the forests especially along the and long isolation from the Central African forests coastal line, mainly for establishing sisal plantations (Rodgers & Homewood 1982). A stable long-term and crop production. climate in combination with high rainfall in tropical About 20 km inland from Pangani an elevation forest areas are usually associated with a high species step of about 50–100 m is apparent. Here at about diversity (Fjeldså & Lovett 1997). A loss of these for- 300 m a.s.l. stretches dense coastal forest belonging ests would result in an enormous loss of biodiversity to the Gendagenda reserve. However, in the past 10 (Newmark 2002). years even here the practice of setting fires to reduce In the vicinity of the studied plots lies the coastal tree cover in favor of grassland was observed. It must town Pangani, which had its greatest importance in be feared that also this patch of indigenous lowland the 19th century. Pangani was the starting and desti- forest will disappear in the near future. nation of caravans coming from or heading for the The aim of this study was to compare the Salta- hinterland, trading with ivory and later with slaves toria composition of intact coastal forest within the (Glassman 1995). In 1880 about 100 000 people Gendagenda reserve with fire-influenced patches of forest and grasslands resulting from intensive burning over the last decades near Mwera village, south of e-mail: [email protected] Pangani (Fig. 1). 53 HEMP FIG. 1. Map of East Africa. Black triangles: study plots 1: fire-maintained grasslands and fire-influenced coastal forests near Mwera. 2: Gen- dagenda forest reserve. RESEARCH AREA some parts of which are already disturbed by infre- quent fires (Fig. 2). The coastal area of Tanzania receives its precipitation Burnt grasslands were investigated directly at the from monsoonal rainfalls from the Indian Ocean co- coast near Pangani, about 20 km southward, next to inciding with the northward and southward passages the small village of Mwera (UTM zone 37 04/99/369 in March to May (long rains with most precipitation) east, 93/94/462 south) (Figs. 1, 2). Plant species com- and October to December (short rains). The district mon in coastal savanna grasslands were the grasses city Tanga receives a total of about 1000 mm per Imperata cylindrica, Digitaria milanjiana, Echinochloa year. haploclada, Setaria incrassata, Panicum infestum and The study area is characterized by huge sisal plan- the herb Kohautia coccinea (A. Hemp unpubl. data). tations about 5–10 km inland, and wide patches of The vegetation cover was 80–100% with a height of burnt grasslands intermingled with remnants of for- about 1m. These grasslands are set on fire nearly every est (East African coastal scrub forest, Burgess & Clarke year before the long rains in March. 2000). Adjacent to the sisal plantations the indige- Remnants of forest are intermingled with the grass- nous forest (East African coastal dry forest, Burgess lands. After frequent fires the fire-tolerant palmtree & Clarke 2000) of the Gendagenda reserve is situated, Hyphaene compressa sprouts. Well adapted to frequent 54 EAST AFRICAN SALTATORIA fires, the South American tree Leucaena latisiliqua becomes dominant in the first years after a fire, form- ing nearly monospecific stands. In the regeneration stage after about 10 to 15 years following a fire indigenous trees like Kigelia africana, Balanites wilsoniana, Lannea schweinfurthii, Xanthoxylum cf. holtzianum, Guettarda speciosa, and Sclerocarya birrea form the tree layer, and shrubs such as Psychotria lauracea, Grewia forbesii, Allophylus rubifolius, Harrisonia abyssinica, Vangueria infausta, Flueggea virosa, Pemphis acidula and Polysphae- ria multiflora are found in the undergrowth (A. Hemp unpubl. data). The canopy is usually 10 m high. All investigated forests remnants along the coast in the FIG. 2. Burnt grassland at the coast near the village area belong to regeneration stages after fire. Some cen- Mwera on the Indian Ocean. In the background the tral parts of these remnants might be more or less un- fire-tolerant palmtree Hyphaene compressa. disturbed by fires, although the patches are mostly not bigger than a few square meters (equivalent to the forest community “coastal scrub forest” in Burgess & Clarke 2000). closed forest. In the closed forest, whether the spe- Areas of undisturbed indigenous lowland forest cies occurred on the forest floor or in the bush or tree mixed with fire-influenced forests were investigated layer was registered. In grasslands, Saltatoria species between Kabuko and Mwera at 350 m a.s.l. (Gen- were identified by sight by walking repeatedly on par- dagenda forest reserve, Fig. 3). This forest type, allel tracks through the plots at distances of about which belongs to legume-dominated dry forest, after 1–1.5 m. Smaller species and those difficult to iden- Burgess & Clarke (2000), was characterized by trees tify were caught by net-sweeping. The abundance of and shrubs such as Brachystegia spiciformis, Milicia gomphocerines was estimated by the male courtship excelsa, Strychnos scheffleri, Hugonia castaneifolia, Po- song. In forest habitats all Saltatoria were caught, as lyaltia stuhlmannii, Kraussia kirkii, Polysphaeria parvi- the density of individuals was generally low. Bushes folia, Psychotria punctata and Pavetta stenosepala (A. and small trees were checked by net-sweeping. The Hemp, unpubl. data). The mean canopy height was check of one plot lasted in general more than 1 hour, 25 m. in forest habitats sometimes more than 2 hours. Near METHODS Saltatoria species composition was recorded for plots of burnt coastal grasslands, for several patches of forest remnants and an adjacent larger forest patch in a regeneration stage (indicated with “1” in Fig. 1), and two plots of dense indigenous forest near the Kabuko- Mwera road (Gendagenda forest reserve, indicated with “2” in Figure 1). All plots were monitored several times (February 1999, January 2000, January and February 2001, December 2004). Four plots were chosen in homogenous grasslands, usually an area of 30 x 30 m. The forest plots had sizes of about 100 x 100 m (two plots within the Gendagenda forest reserve, one plot in regeneration stage, three fire-influenced plots). FIG. 3. Coastal forest area at 300 m a.s.l. between Ka- In the forest plots it was noted in which micro- buko and Mwera. In the background the Gendagenda habitat each species occurred. A differentiation was Hill. In the foreground fire impact along the road side made between forest edge (clearing or road side) and vegetation. 55 HEMP TABLE 1. List of Saltatoria. Data on habitat and distribution. Gr: grassland species, Fe: forest edge species, F: forest species, Dis: distribution, EA: species restricted to East Africa, C: species restricted to coastal habitats (coastal endemics), remaining species: widespread; Loc: 1: coastal forest remnants and grasslands near Mwera; 2: Gendagenda forest reserve (as shown on Fig. 1). Species/Family Habitat Gr Fe F Dis loc Family Tetrigidae Paratettix africanus Bolivar, 1908 Open patches in humid grasslands x 1 Family Eumastacidae Plagiotriptus

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